The performance of a microwave or other high-frequency integrated circuit (IC) can be verified using various testing techniques. In most instances, however, the preferred technique is to obtain measurements with a vector network analyzer. A vector network analyzer yields the complex impedance of an IC or other circuit at a given frequency, measuring the amplitude and phase difference between a network response signal and a reference signal. The amplitude and phase difference are key measurements for verifying the form of the particular transfer function that characterizes a specific RF/microwave circuit or system. The information provided by the vector network analyzer measurements can be used, for example, for precision calibration of the microwave test setup without the confounding effects typically introduced as a result of the parasitic effects induced by test cables, connectors, or from other sources of error in a microwave test system.
The testing and verification of high-frequency ICs typically involves small-signal characterization of RF and/or microwave components of the circuit or system. There is fairly wide-spread agreement that a preferred small-signal characterization of RF and microwave components is the one that is based on scattering parameters, typically referred to as s-parameters. The s-parameters comprise a set of parameters that describe the scattering and reflection of traveling electromagnetic (em) waves that occur, for example, when a network is inserted into a transmission line. The s-parameters are typically used to characterize high-frequency networks, especially because simpler models that are valid at lower frequencies are usually inadequate in the case of high-frequency networks. The s-parameters are normally measured as a function of frequency, the measurement representing a complex gain (i.e., magnitude and/or phase). Accordingly, s-parameters are often termed complex scattering parameters. The resulting measurement is typically in decibels 20 log(Sij) since s-parameters are voltage ratios of the corresponding electromagnetic power waves.
The s-parameters can be used to accurately describe the electronic behavior of a device under linear conditions in the microwave frequency range. Typically, s-parameters are measured in 50 ohm transmission systems and require no opens or shorts in order to be connected with a device-under-test (DUT). The testing of an IC or other system ordinarily is accomplished by attaching to a vector network analyzer an s-parameter measurement unit that provides for microwave signal switching, sampling, and load-terminating.
Conventional techniques for determining the s-parameters typically require 1) a system calibration activity and 2) a direct, accurate measurement, followed by 3) a device measurement extraction, device calibration or other “de-embedding procedure”—typically implemented in a software-based module. This third activity is typically critical for removing the testing fixture characteristics from the overall measurement. The calibration procedure measures known precision standards and extracts an “error model” to represent the magnitude and phase errors in the test equipment and the connections to the DUT. When the electronic response of the DUT is measured, the “raw data” obtained is adjusted by subtracting the effects of the test equipment, thereby “de-embedding” the true device data by subtracting out the effects of the error model.
Various attempts have been made over the years to reduce the costs associated with such testing procedures and techniques. Notwithstanding these attempts, however, there remains a need for an effective and efficient on-chip embedded test technique that can obviate the parasitic effects that are inevitably caused by contact pads and related interactions between pads, RF probes, and RF cables that connect to the necessary test equipment. Without an effective and efficient on-chip embedded test technique, complex calibration procedures are typically required in order to factor out the effect of unwanted parasitic circuit elements. So, too, without an effective and efficient on-chip embedded test technique, test equipment with high precision as well as a wide dynamic range—and, accordingly, involving significant costs—is needed to measure RF/microwave performance and attain a proper calibration.